(1) Field of the Invention
This invention relates to a heater in which a heating element is embedded in a ceramic substrate and a method of manufacturing the same for treating a substance to be heated, such as semiconductor wafer.
(2) Related Art Statement
Attention is now paid to dense ceramics as a substrate for an electrostatic chuck. In equipment for manufacturing a semiconductor, a halogen corrosive gas such as ClF.sub.3 is frequently used as an etching gas or a cleaning gas. Moreover, for rapidly heating and cooling a semiconductor wafer while holding it, it is desired that a substrate of an electrostatic chuck has a high heat conductivity and a thermal shock-resistance to prevent destruction due to rapid thermal changes. Dense aluminum nitride has high corrosive-resistance against the above halogen corrosion gas. Moreover, aluminum nitride is known as a material with high thermal conductivity with a volume resistivity of 10.sup.14 .OMEGA.cm or over at room temperature and high thermal shock-resistance. It is therefore considered preferable that a substrate of an electrostatic chuck as an equipment for manufacturing a semiconductor is formed of an aluminum nitride sintered body. It is proposed that a substrate of a ceramic heater or a heater with a built-in high frequency electrode is formed of an aluminum nitride.
NGK Insulators, Ltd. discloses in Japanese examined patent publication No. 7-50736 that a resistance heating element and an electrostatic chuck electrode are embedded in a substrate of aluminum nitride or a resistance heating element and an electrode for generating a high frequency are embedded therein.
When a resistance heating element and a high frequency electrode were embedded in a aluminum nitride substrate to make an electrode for generating high frequency waves and the electrode was operated at a high temperature, for example, 600.degree. C. or over, the state of the high frequency waves or the state of the high frequency plasma often became unstable. Moreover, when a resistance heating element and an electrostatic chuck electrode were embedded in the aluminum nitride substrate to make an electrostatic chuck and the equipment was operated at a high temperature, for example, 600.degree. C. or over, the electrostatic adsorption power in the electrostatic chuck became unstable locally or with the passage of time.